This invention relates to an optical backscattering meter including an optical transmitter whose transmission power is modulated (wobbled) with a variable frequency via an oscillator and whose transmission beam is led into a light wave cable (LWL) via a beam splitter, and including an optical receiver arranged as a photodiode, to which receiver are applied via the beam splitter portions of the transmission beam that are scattered back from the light wave cable (LWL) and in which a mixing signal is formed from a signal proportional to the optical backscattering power and a modulation voltage having the oscillator frequency and is evaluated for determining the location of the backscattering and the intensity of the backscattering.
In such an arrangement, known from the U.S. Pat. No. 4,320,968 (3/23/82), electrical output signal of the photodiode and the oscillator signal are together applied to a mixer to form the mixing signal. Since high modulation frequencies are required, a very "fast" and consequently costly detecting circuit is necessary.